1. Field of the Invention
The present invention relates to a technique for handling a jet pump located in a downcomer portion of a boiling water reactor, and in particular, to a bolt fixing device of a jet pump beam capable of performing attaching/detaching operations of a jet pump inlet mixer simply and in a short time.
2. Description of the Related Art
A boiling water reactor includes an external circulation system for forcing a coolant into a reactor core, and a jet pump connected to the external circulation system is provided in a reactor pressure vessel. A plurality of sets of jet pumps are provided in an annular downcomer portion between the reactor pressure vessel and a core shroud.
The jet pump, as described in Patent Document 1 (Japanese Patent Laid-Open Publication No. 2005-233864), is provided for the downcomer portion in the reactor pressure vessel and mainly includes a riser, a diffuser and an inlet mixer. The jet pump is installed in order of the riser, the diffuser and the inlet mixer when located in the reactor pressure vessel.
Installation of the inlet mixer is performed as follows.
First, a lower end of the inlet mixer is passed through a riser bracket which is installed on a pipe side of the riser, a nozzle side portion of the inlet mixer formed with a turn-around path is inserted into an opening of the top portion of the diffuser, a seat surface of an elbow of the inlet mixer is placed on the top portion of the riser, a head bolt of a jet pump beam for installation of the inlet mixer is tightened, and the inlet mixer is located on an upper portion of the riser.
The inlet mixer is tightened and installed to the top of the riser by means of head bolt with the jet pump beam, and thereafter, rotation preventing operation of the head bolt screwed into the jet pump beam should be performed.
For this reason, in the bolt fixing device of a conventional jet pump beam, the head bolt of the jet pump beam attached to the top of the inlet mixer is screwed for tightening, and after fixing the inlet mixer to the top of the riser, a keeper, an inside of which has the same hexagonal face as that of a hexagon bolt head of the upper portion of the head bolt, is placed through the head bolt and is then firmly attached to a plate of the upper surface of the jet pump beam. Then, after being firmly attached to the plate, the keeper and the plate are welded together through a welding operation so as to prevent the rotation of the head bolt.
In the bolt fixing device of the conventional jet pump beam as mentioned above, it is necessary to release the rotation prevention structure of the head bolt and weld the keeper to the plate for preventing the rotation of the head bolt again in every detaching and reinstalling operation of the inlet mixer from the jet pump. In addition, for the attaching/detaching operations of the inlet mixer, a welding working is to be performed by an underwater remote operation having inferior working conditions, so that a considerably long working time is required, thus making it difficult and complicated to perform the attaching/detaching handling operations of the inlet mixer.